1. Field of the Invention
The present invention relates to a method of forming a pattern. More particularly, the present invention relates to a method of forming a pattern that is suitable for use in, for example, a semiconductor production process for an IC or the like, a circuit board production process for a liquid crystal, a thermal head or the like and other photoapplication lithography processes. In particular, the present invention relates to a method of forming a pattern that is suitable for the lithography using an ArF exposure apparatus or liquid-immersion projection exposure apparatus in which a far-ultraviolet light of wavelength 300 nm or shorter is employed as a light source.
2. Description of the Related Art
Since the development of the resist for a KrF excimer laser (248 nm), a pattern forming method based on chemical amplification has been employed as a resist patterning method in order to compensate for any sensitivity decrease caused by light absorption. A positive pattern forming method based on chemical amplification will be described by way of example. In this pattern forming method, the acid generator contained in exposed areas is decomposed upon exposure to light, such as an excimer laser, electron beams or an extreme ultraviolet light, to thereby generate an acid. In the stage of the bake after the exposure (Post-Exposure Bake: PEB), the generated acid is utilized as a reaction catalyst so that alkali-insoluble groups are converted to alkali-soluble groups. Thereafter, the exposed areas are removed by an alkali developer.
For use in the above method, various alkali developers have been proposed. For example, an aqueous alkali developer containing 2.38 mass % TMAH (aqueous solution of tetramethylammonium hydroxide) is universally used.
Moreover, the shortening of the wavelength of exposure light sources and the realization of high numerical apertures (high NA) for projector lenses have been advanced in order to cope with the miniaturization of semiconductor elements. To now, an exposure unit using an ArF excimer laser of 193 nm wavelength as a light source has been developed. Further, a method, known as a liquid-immersion method, in which the space between a projector lens and a sample is filled with a liquid of high refractive index (hereinafter also referred to as an “immersion liquid”) has been proposed as a technology for enhancing the resolving power. Still further, an EUV lithography or the like in which exposure is carried out using an ultraviolet of further shorter wavelength (13.5 nm) has been proposed.
In another aspect, not only the currently mainstream positive type but also negative chemically amplified resist compositions for use in the pattern formation by alkali development are being developed (see, for example, patent references 1 to 4). This reflects the situation in which in the production of semiconductor elements and the like, while there is a demand for the formation of a pattern with various configurations, such as a line, a trench and a hole, there exist patterns whose formation is difficult with the use of current positive resists.
Also, the development of negative resist developers is being promoted. For example, patent reference 5 discloses using as a developer a negative developer comprising an organic solvent in which the content of metal impurities is controlled at a given value or less in order to realize a pattern formation exhibiting a high sensitivity, excelling in the resolution of trench pattern and ensuring favorable iso/dense bias.
Moreover, a double development technique as a double patterning technology capable of enhancing the resolving power is described in patent reference 6 and patent reference 7. In this technique, using the phenomenon that upon exposure, the polarity of the resin contained in the resist composition becomes high in a region of high light intensity while the polarity of the resin is kept low in a region of low light intensity, the region of high exposure in a specified resist film is dissolved by a developer of high polarity while the region of low exposure is dissolved by a developer comprising an organic solvent. Thus, the region of intermediate exposure amount remains undissolved away during the development, so that a line-and-space pattern with a half pitch of exposure mask is formed.